An octahedral coordination complex has a crystal field stabilization energy (CFSE) of -1.2 _o and a spin-only magnetic moment of approximately 3.87 BM . Which of the following complexes matches these properties?

Step-by-step solution

The spin-only magnetic moment is given by = n(n+2) BM , where n is the number of unpaired electrons. Given 3.87 BM , we have n(n+2) = 3.87 n = 3 unpaired electrons. Let us evaluate the given complexes: For [ Co ( H ₂ O )₆ ]²⁺ : Co ²⁺ is a 3 d ^7 ion. H ₂ O is a weak field ligand, so the configuration is t_ 2g ^5 e_g^2 . Number of unpaired electrons n = 3 . CFSE = [5(-0.4) + 2(0.6)] _o = -0.8 _o . For [ Mn ( CN )₆ ]⁴⁻ : Mn ²⁺ is a 3 d ^5 ion. CN ^- is a strong field ligand, so the configuration is t_ 2g ^5 e_g^0 . N